subroutine flat4(s,npts,nflatten) ! Flatten a spectrum for optimum display ! Input: s(npts) Linear scale in power ! nflatten If nflatten=0, convert to dB but do not flatten ! Output: s(npts) Flattened, with dB scale implicit real*8 (a-h,o-z) real*4 s(6827) real*4 base real*8 x(1000),y(1000),a(5) data nseg/10/,npct/10/ if(s(1).gt.1.e29) go to 900 !Boundary between Rx intervals: do nothing do i=1,npts s(i)=10.0*log10(s(i)) !Convert to dB scale enddo if(nflatten.eq.0) go to 900 nlen=npts/nseg !Length of test segment i0=npts/2 !Midpoint k=0 do n=2,nseg !Skip first segment, likely rolloff here ib=n*nlen ia=ib-nlen+1 if(n.eq.nseg) ib=npts call pctile(s(ia),ib-ia+1,npct,base) !Find lowest npct of points in segment do i=ia,ib if(s(i).le.base) then if (k.lt.1000) k=k+1 !Save these "lower envelope" points x(k)=i-i0 y(k)=s(i) endif enddo enddo kz=k a=0. nterms=3 call polfit(x,y,y,kz,nterms,0,a,chisqr) !Fit a low-order polynomial do i=1,npts t=i-i0 yfit=a(1)+t*(a(2)+t*(a(3)+t*(a(4)+t*(a(5))))) s(i)=s(i)-yfit !Subtract the fitted baseline enddo 900 return end subroutine flat4